Embryonal carcinoma cells (EC cells), the stem cells of teratocarcinomas represent a useful in vitro system to study certain cellular and molecular aspects of early mammalian embryogenesis. This is due to unique properties which EC cell lines share with embryonic stem cells, such as the ability to differentiate into various cell types and to participate in the formation of chimeric animals. While EC cells are malignant, their differentiate derivatives are non-malignant. We propose to study, the gene expression level, the in vitro inducible differentiation of the EC cell lines F9 and P19 into extraembryonic and embryonic cell lineages. 1. The regulation of expression of the major histocompatibility (H2) antigens during F9 and P19 differentiation into various cell types will be studied using H2 antibodies and cDNA probes. Cloned H2 genes will be transferred into F9 and P19 cells. The expression of the transferred and endogenous H2 genes during differentiation will be compared. 2. DNAs complementary to mRNAs (cDNAs) enriched for in EC stem cells or in EC derived differentiated cells will be isolated from cDNA libraries. The cDNA clones will be used to analyze changes in steady state levels and synthesis rates of the corresponding mRNAs during differentiation. 3. A method of insertion mutagenesis of EC cells has been developed using Moloney murine leukemia virus (MLV) infection. Differentiation defective EC cell mutants will be isolated from populations mutageneized with MLV. From these mutants, genes adjacent to the insertion mutagen will be isolated for functional studies. These studies might provide some insight into the relationships between specific gene expression, cell proliferation and cell differentiation in embryogenesis and neoplasia.